[a sequel to Rainer Weiss’s colloquium about the opening of gravitational wave astronomy] LIGO’s discovery of gravitational waves from colliding black holes has opened the high-frequency (10 Hz to 10,000 Hz) gravitational window onto the universe. Over the next two decades the volume of the universe that LIGO and its interferometric partners can search may increase by a factor ~30,000, and three more gravitational windows will likely be opened: The low-frequency band (periods of minutes to hours) by space-based detectors such as LISA (the Laser Interferometer Space Antenna); The very-low-frequency band (periods of years) by the timing of arrays of radio pulsars; and The extremely-low-frequency band (periods of billions of years) by mapping the polarization of the cosmic microwave background. This lecture will describe these gravitational wave detectors and some of the sources they may see and science that may be extracted from their observations.